Described in US-A 2012/0192658, US-A 2011/0146416, US-A 2011/0167907, US-A 2011/0265580, and US-A 2014/0000374 patents are measuring transducers of the vibration-type, which are adapted to produce reaction forces for example, namely density dependent inertial forces and/or mass flow rate dependent Coriolis forces and/or viscosity dependent friction forces—thus forces dependent on at least one physical, measured variable—, for example, namely a density and/or a mass flow rate and/or a viscosity—of a fluid flowing in a pipeline, or which are provided to be used as a component of a vibronic measuring device serving for measuring said measured variable. Each of the disclosed measuring transducers comprises a tube arrangement with four measuring tubes for conveying flowing fluid as well as two mutually spaced flow dividers having, in each case, a tubular chamber adapted for guiding in- and outflowing fluid. The measuring tubes are connected to each of the chambers for forming flow paths for parallel flow, wherein each of the chambers has a chamber floor, in which exactly four mutually spaced flow openings are formed communicating with a lumen of the chamber, and each of the four measuring tubes is connected with a respective inlet-side, first measuring tube end with one of the flow openings of the respective first flow divider, consequently communicates with its lumen and with a respective outlet-side, second measuring tube end with one of the flow openings of the respective second flow divider, consequently communicates with its lumen. The four measuring tubes are embodied, in each case, at least sectionally straight and/or at least sectionally bent, for example, in the form of a “U” or a “V”, for example, also in such a manner that they are, such as shown in US-A 2011/0146416, in each case, straight over an entire measuring tube length. Additionally, the measuring tubes can be so formed and arranged that the tube arrangement has at least two imaginary symmetry planes perpendicular to one another, relative to which the tube arrangement is, in each case, mirror symmetric.
Each of the measuring transducers includes additionally, in each case, an electromechanical exciter mechanism serving for exciting mechanical oscillations of the measuring tubes as well as a sensor arrangement serving both for registering oscillatory movements of the measuring tubes as well as also for generating at least one oscillation measurement signal representing oscillations of the measuring tubes.
The above-mentioned two flow dividers of each of the measuring transducers can, in each case, also be an integral component of a transducer housing, namely a transducer housing having a cavity with tube—, exciter—as well as sensor arrangement placed therein, in such a manner that a first housing end of the transducer housing is formed by means of the first flow divider and a second housing end of the transducer housing is formed by means of the second flow divider and that the transducer housing has, laterally bounding the particular cavity, a side wall, which is affixed both to the first flow divider as well as also to the second flow divider.
Furthermore, each of the disclosed measuring transducers can, additionally, for the purpose of forming a vibronic measuring system, for example, in the form of an in-line-measuring device in compact construction, serving for measuring at least one measured variable, for example, namely one of the flow parameters, mass flow rate and volume flow rate or one of the substance parameters, density and viscosity, of a fluid flowing in a pipeline, in each case, additionally be electrically connected to an associated measuring—and operating electronics serving for operating the exciter mechanism as a well as for processing the at least one oscillation measurement signal delivered by the sensor arrangement, especially namely for ascertaining measured values for the at least one measured variable from the at least one oscillation measurement signal.
As discussed in the above mentioned US-A 2012/0192658, accuracy of measurement of such a measuring system formed by means of a measuring transducer of the above indicated type, namely accuracy with which the measured values generated by means of the measuring system for the at least one measured variable agree with the measured variable, can be optimized by selecting geometry and surface characteristics of the measuring tubes such that a flow resistance of all four measuring tubes is identical. Said condition is naturally fulfilled, also over a comparatively broad measuring or operating range, in the case of the tube arrangements disclosed in US-A 2011/0146416, US-A 2011/0167907, US-A 2011/0265580, and US-A 2014/0000374, namely, in each case, tube arrangements formed by means of four equally-constructed measuring tubes and being, in each case, mirror symmetrical relative to three imaginary, mutually orthogonal, symmetry planes. In the case of tube arrangements formed by means of four bent, for example, U-, respectively V-shaped, measuring tubes only pairwise equally-constructed, equally as well, in each case, mirror symmetrical relative to only two mutually orthogonal imaginary symmetry planes, again, flow resistances identical in the above-mentioned sense can be achieved according to the US-A 2012/0192658 for a certain operating or working point, in that all four measuring tubes have, in each case, equal surface characteristics and additionally are at least of equal measuring tube length and equal caliber.
Although use of four measuring tubes arranged and embodied according to one of the above-mentioned principles for certain measuring or operating ranges can achieve quite acceptable measurement accuracies, it has nevertheless been found that for certain applications considerably lessened measurement accuracies can be observed; this not least of all also in the case of applications, in which the at least one measured variable is to be ascertained for a fluid flowing with a comparatively high mass flow rate of some thousands of tons per hour and/or a fluid flowing with a strongly fluctuating Reynolds number, namely a Reynolds number changing over a wide range and/or very quickly with time, wherein a measuring system formed by means of a measuring transducer embodied according to US-A 2012/0192658 can have an accuracy of measurement tending to be fragile to a higher degree in comparison with measuring systems disclosed in US-A 2011/0146416, US-A 2011/0167907, US-A 2011/0265580, and US-A 2014/0000374.